On 2 Okt., 00:53, n...@puntnl.niks (Nico Coesel) wrote:> Klaus Kragelund <klausk...@hotmail.com> wrote: > >Hi > > >I need a CMOS gate with low voltage drop at about 30mA current source and s= > >ink. The tiny logic NL27WZ14 has 600mV drop at 32mA which equates to 18ohm = > >RDS on. > > Maybe look for a MOSFET driver chip. >that was my first thought, something like fan3111, but.. datasheet doesn't say what the dropout is, it maybe a bit slow for 10MHz and who knows how much power it will use maybe a buffer/linedriver -Lasse
Low RDSon Logic CMOS Gate
Started by ●October 1, 2012
Reply by ●October 2, 20122012-10-02
Reply by ●October 2, 20122012-10-02
On 2 Okt., 02:04, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> On Mon, 01 Oct 2012 12:35:52 -0600, hamilton <hamil...@nothere.com> > wrote: > > >On 10/1/2012 11:46 AM, John Larkin wrote: > >> On Mon, 01 Oct 2012 10:42:16 -0700, Jim Thompson > > >>> How about a 6-pack of '04's paralleled? > > >>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 ...Jim Thompson> > >> Massive shoot-through. > > >Please describe shoot-through. > > If a CMOS gate's input is roughly midway between Vcc and ground, both > p-channel and n-channel fets can be partially turned on in the front > end. Current "shots through" the fets from Vcc to ground. That can > draw a lot of supply current and potentially heat up the chip. It > always happens briefly when a normal, fast input transitions, but it > can get much worse if an input transitions slowly, or parks at an > intermediate voltage. Schmitt-trigger gates are designed for slow > inputs, so generally have moderate peak shoot-through currents. > > Paralleling Schmitts is interesting. At some input voltage, some of > the gates will see a "1" and some may see a "0", so their paralleled > outputs will fight one another and pull a *lot* of supply current. > Running the signal through one Schmitt section, and then driving a > bunch more sections in parallel, is safer. > > We almost fried some Tiny Logic gates, powering them from +5 but > driving them from 3.3 volt logic from an FPGA. They got really hot. >HC or HCT ? http://www.ti.com/lit/ds/symlink/sn74hct04.pdf http://www.nxp.com/documents/data_sheet/74HC_HCT04.pdf TI <3mA per pin at 2.4Vin NXP <590uA at 2.9Vin that shouldn't be a problem driven with a 3.3V output -Lasse
Reply by ●October 2, 20122012-10-02
On Tue, 2 Oct 2012 06:35:42 -0700 (PDT), "langwadt@fonz.dk" <langwadt@fonz.dk> wrote:>On 2 Okt., 02:04, John Larkin ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> On Mon, 01 Oct 2012 12:35:52 -0600, hamilton <hamil...@nothere.com> >> wrote: >> >> >On 10/1/2012 11:46 AM, John Larkin wrote: >> >> On Mon, 01 Oct 2012 10:42:16 -0700, Jim Thompson >> >> >>> How about a 6-pack of '04's paralleled? >> >> >>> � � � � � � � � � � � � � � � � � � � � ...Jim Thompson >> >> >> Massive shoot-through. >> >> >Please describe shoot-through. >> >> If a CMOS gate's input is roughly midway between Vcc and ground, both >> p-channel and n-channel fets can be partially turned on in the front >> end. Current "shots through" the fets from Vcc to ground. That can >> draw a lot of supply current and potentially heat up the chip. It >> always happens briefly when a normal, fast input transitions, but it >> can get much worse if an input transitions slowly, or parks at an >> intermediate voltage. Schmitt-trigger gates are designed for slow >> inputs, so generally have moderate peak shoot-through currents. >> >> Paralleling Schmitts is interesting. At some input voltage, some of >> the gates will see a "1" and some may see a "0", so their paralleled >> outputs will fight one another and pull a *lot* of supply current. >> Running the signal through one Schmitt section, and then driving a >> bunch more sections in parallel, is safer. >> >> We almost fried some Tiny Logic gates, powering them from +5 but >> driving them from 3.3 volt logic from an FPGA. They got really hot. >> > >HC or HCT ? > >http://www.ti.com/lit/ds/symlink/sn74hct04.pdf >http://www.nxp.com/documents/data_sheet/74HC_HCT04.pdf > >TI <3mA per pin at 2.4Vin >NXP <590uA at 2.9Vin > >that shouldn't be a problem driven with a 3.3V output > >-LasseNL37WZ16. All three sections in parallel. The US8 package doesn't get rid of heat very well. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Reply by ●October 2, 20122012-10-02
On Monday, October 1, 2012 1:01:52 PM UTC-7, Klaus Kragelund wrote:> On Monday, October 1, 2012 9:52:19 PM UTC+2, whit3rd wrote: > > > On Monday, October 1, 2012 10:33:01 AM UTC-7, Klaus Kragelund wrote:> > > I need a CMOS gate with low voltage drop at about 30mA current source and sink. > > One can use discrete complementary MOSFETs to make a CMOS-like inverter,> I have 3.3V, can make 5V if I need to. This is for a high efficiency device, so any powerloss is critical. Shoot through if a FET pair can easily go up to several amps, which won't be noticed if you are not looking.A dual MOSFET (P-channel/N-channel pair) like Rohm EM6M2 can easily handle the task. If you add a couple of 2 ohm drain resistors, it limits the shoot-through to well under one amp, but the output resistance only gets two ohms drop (still well below your 5 ohm goal for 3.3V power supplies). Note the PFET has rather high capacitance, that's required to get the low on-resistance. For best shoot-through limit, it gets complicated (you need something more than a logic drive, it takes turn-on delayed but turn-off prompt).
Reply by ●October 2, 20122012-10-02
On Wednesday, October 3, 2012 12:04:57 AM UTC+2, whit3rd wrote:> On Monday, October 1, 2012 1:01:52 PM UTC-7, Klaus Kragelund wrote: > > > On Monday, October 1, 2012 9:52:19 PM UTC+2, whit3rd wrote: > > > > > > > On Monday, October 1, 2012 10:33:01 AM UTC-7, Klaus Kragelund wrote: > > > > > > > I need a CMOS gate with low voltage drop at about 30mA current source and sink. > > > > One can use discrete complementary MOSFETs to make a CMOS-like inverter, > > > > > I have 3.3V, can make 5V if I need to. This is for a high efficiency device, so any powerloss is critical. Shoot through if a FET pair can easily go up to several amps, which won't be noticed if you are not looking. > > > > A dual MOSFET (P-channel/N-channel pair) like Rohm EM6M2 can easily handle the task. > > If you add a couple of 2 ohm drain resistors, it limits the shoot-through to well under one > > amp, but the output resistance only gets two ohms drop (still well below your 5 ohm > > goal for 3.3V power supplies). Note the PFET has rather high capacitance, that's > > required to get the low on-resistance. > >..Snip.. The EM6M2 has 1nC of gate charge. Running that at 5V and 200kHz will consume 1mW. I was trying to reduce the gate charge losses by using a logic IC On that subject, anyone know the value of the gate charge for a run-of-the-mill gate inside a chip? Regards Klaus
Reply by ●October 2, 20122012-10-02
On Oct 1, 8:18=A0pm, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> On Mon, 1 Oct 2012 16:49:41 -0700 (PDT), dagmargoodb...@yahoo.com > wrote: > > > > > > > > > > >On Oct 1, 1:33 pm, Klaus Kragelund <klausk...@hotmail.com> wrote: > >> Hi > > >> I need a CMOS gate with low voltage drop at about 30mA current source =and sink. The tiny logic NL27WZ14 has 600mV drop at 32mA which equates to 1= 8ohm RDS on.> > >> I am searching for a device with less than 5-10 ohms and it would need=to be ok to parallel to get lower resistance. Also, it must not have to mu= ch crossover shoot-through (so probably schmitt trigger type) and must have= low dissipation at high operational frequency (1-10MHz)> > >> Any one have a part in mind? > > >> Thanks > > >> Klaus > > >http://www.intersil.com/en/products/switches-muxs-crosspoints/low-vol... > > >(from John Devereux, earlier this year) > > >Break-before-make. > > >DigiKey had competing parts, too. > > But look at the capacitances! There's no free lunch.For sure there are higher Rds(on) parts with lower capacitances, right? I was just throwing out an extreme example, since I'm an extremist :-). I suspect the make-before-break convenience, integration, and capacitances in other switches will be attractive. I didn't have time to screen parts--I mostly have to post and run these days. James
Reply by ●October 2, 20122012-10-02
On Oct 1, 10:09=A0pm, "Vladimir Vassilevsky" <nos...@nowhere.com> wrote:> "John Larkin" <jjlar...@highNOTlandTHIStechnologyPART.com> wrote in messa=ge> > news:n5bk68h59kckkcmb8ntr5ecfauefjkmq6l@4ax.com... > > > If a CMOS gate's input is roughly midway between Vcc and ground, both > > p-channel and n-channel fets can be partially turned on in the front > > end. > > This problem is greatly overstated. > While ago I tested static cross conduction of HCT04 gate powered at +5V. > The worst case was about 4mA, at 0.9V at the input. > > Vladimir Vassilevsky > DSP and Mixed Signal Consultantwww.abvolt.comI've destroyed 74AC parts that way. Smoked 'em. -- Cheers, James Arthur
Reply by ●October 3, 20122012-10-03
On Tue, 2 Oct 2012 19:43:44 -0700 (PDT), dagmargoodboat@yahoo.com wrote:>On Oct 1, 10:09�pm, "Vladimir Vassilevsky" <nos...@nowhere.com> wrote: >> "John Larkin" <jjlar...@highNOTlandTHIStechnologyPART.com> wrote in message >> >> news:n5bk68h59kckkcmb8ntr5ecfauefjkmq6l@4ax.com... >> >> > If a CMOS gate's input is roughly midway between Vcc and ground, both >> > p-channel and n-channel fets can be partially turned on in the front >> > end. >> >> This problem is greatly overstated. >> While ago I tested static cross conduction of HCT04 gate powered at +5V. >> The worst case was about 4mA, at 0.9V at the input. >> >> Vladimir Vassilevsky >> DSP and Mixed Signal Consultantwww.abvolt.com > >I've destroyed 74AC parts that way. Smoked 'em.HCT stuff isn't tuned for speed so has little crossover current (none, ideally). AC logic is a whole different kettle. Better decouple AC gates well. ;-)
Reply by ●October 3, 20122012-10-03
On Tue, 2 Oct 2012 19:42:45 -0700 (PDT), dagmargoodboat@yahoo.com wrote:>On Oct 1, 8:18�pm, John Larkin ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> On Mon, 1 Oct 2012 16:49:41 -0700 (PDT), dagmargoodb...@yahoo.com >> wrote: >> >> >> >> >> >> >> >> >> >> >On Oct 1, 1:33 pm, Klaus Kragelund <klausk...@hotmail.com> wrote: >> >> Hi >> >> >> I need a CMOS gate with low voltage drop at about 30mA current source and sink. The tiny logic NL27WZ14 has 600mV drop at 32mA which equates to 18ohm RDS on. >> >> >> I am searching for a device with less than 5-10 ohms and it would need to be ok to parallel to get lower resistance. Also, it must not have to much crossover shoot-through (so probably schmitt trigger type) and must have low dissipation at high operational frequency (1-10MHz) >> >> >> Any one have a part in mind? >> >> >> Thanks >> >> >> Klaus >> >> >http://www.intersil.com/en/products/switches-muxs-crosspoints/low-vol... >> >> >(from John Devereux, earlier this year) >> >> >Break-before-make. >> >> >DigiKey had competing parts, too. >> >> But look at the capacitances! There's no free lunch. > >For sure there are higher Rds(on) parts with lower capacitances, >right? I was just throwing out an extreme example, since I'm an >extremist :-). > >I suspect the make-before-break convenience, integration, and >capacitances in other switches will be attractive. > >I didn't have time to screen parts--I mostly have to post and run >these days. > >JamesEven a break-before-make CMOS analog switch has several CMOS gate driver sections, each of which will have shoot-through. Then the final switch capacitance behaves just like a Cpd effect, wasting energy on every transition. No free lunch. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Reply by ●October 4, 20122012-10-04
On Oct 3, 1:48=A0pm, John Larkin <jlar...@highlandtechnology.com> wrote:> On Tue, 2 Oct 2012 19:42:45 -0700 (PDT), dagmargoodb...@yahoo.com > wrote: > > > > > > > > > > >On Oct 1, 8:18 pm, John Larkin > ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> On Mon, 1 Oct 2012 16:49:41 -0700 (PDT), dagmargoodb...@yahoo.com > >> wrote: > > >> >On Oct 1, 1:33 pm, Klaus Kragelund <klausk...@hotmail.com> wrote: > >> >> Hi > > >> >> I need a CMOS gate with low voltage drop at about 30mA current sour=ce and sink. The tiny logic NL27WZ14 has 600mV drop at 32mA which equates t= o 18ohm RDS on.> > >> >> I am searching for a device with less than 5-10 ohms and it would n=eed to be ok to parallel to get lower resistance. Also, it must not have to= much crossover shoot-through (so probably schmitt trigger type) and must h= ave low dissipation at high operational frequency (1-10MHz)> > >> >> Any one have a part in mind? > > >> >> Thanks > > >> >> Klaus > > >> >http://www.intersil.com/en/products/switches-muxs-crosspoints/low-vol=...> > >> >(from John Devereux, earlier this year) > > >> >Break-before-make. > > >> >DigiKey had competing parts, too. > > >> But look at the capacitances! There's no free lunch. > > >For sure there are higher Rds(on) parts with lower capacitances, > >right? =A0I was just throwing out an extreme example, since I'm an > >extremist :-). > > >I suspect the make-before-break convenience, integration, and > >capacitances in other switches will be attractive. > > >I didn't have time to screen parts--I mostly have to post and run > >these days. > > >James > > Even a break-before-make CMOS analog switch has several CMOS gate > driver sections, each of which will have shoot-through. Then the final > switch capacitance behaves just like a Cpd effect, wasting energy on > every transition. No free lunch.The lunch doesn't have to be free. If it's smaller, cheaper, and all wrapped up in a nicer box, that counts too. -- Cheers, James Arthur
